given you want to sweep within one TX bandwidth (which is the complex sampling rate), something like the following flow graph fed into a USRP sink tuned to the right center frequency:
If you want your sweep to span more than the sampling rate, things get more complicated.
Basically, you'd have to retune. However, retuning the local oscillator used to mix up your baseband signal, no matter how it's done, is "slow" compared to a single sample interval. You will inevitably get some gaps or other irregularities.
The USRPs typically have two sampling rates that are relevant to the user: the sampling rate at which you feed in samples from your PC, and the master clock rate, which boils down to the rate at which the DAC/ADC runs at. Imagine the MCR being at least as large as the analog (blue) bandwidth
below:
Within the bandwidth defined by the MCR (and analog anti-imaging filters), you can tune very quickly – but for the B210, in the single channel case, it's 61.44 MHz and in the dual channel case 56 MHz, so you're not winning Gigahertzes of "fast tunable range". Bonus is that this digital offset tuning can be done with timed commands, i.e. you can send a message to the USRP sink block that tells the USRP to tune *exactly* at this and that sample time.
Unlike other devices, the B2xx can't currently tune the LO frequency
with a timed command. Best regards,
Marcus
On 29.04.2016 00:16, Dan McKenna wrote:
Hi There,
I am using a B210 to record band widths from 1 to 20 MHZ, center frequencies from 400Mhz to 2 Ghz.
To test my post detection software I would like to use a Tx channel to make a sweep generator as a real time test source
at sweep rates of around 50 Mhz/second over 1 to 20 mhz range with a center frequency of 400 Mhz to 2Ghz.
To be clear I wish to use companion to generate a frequency sweep at a rate, defined by start/stop frequency and sweep time
or frequency, range, rate..... for example Freq 400 Mhz, range 2 mhz, rate 50Mhz/second.
Is this possible with the standard gnu radio companion block set?
Thanks
Dan
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